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Akira Fujishima

Other affiliations: Kanagawa University, Jilin University, University of Tokyo  ...read more
Bio: Akira Fujishima is an academic researcher from Tokyo University of Science. The author has contributed to research in topics: Photocatalysis & Diamond. The author has an hindex of 70, co-authored 299 publications receiving 69335 citations. Previous affiliations of Akira Fujishima include Kanagawa University & Jilin University.


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Journal ArticleDOI
TL;DR: In this article, the effect of light intensity on the generation efficiency of active oxidative species was examined by measuring the fluorescence derived by the reaction with either coumarin or terephthalic acid.

1,050 citations

Journal ArticleDOI
TL;DR: In this paper, a thin transparent titanium dioxide (TiO2) film was used for the degradation of E. coli cells, which is a pyrogenic constituent of Escherichia coli (E. coli).
Abstract: To examine the special features of the antibacterial effect for a thin transparent titanium dioxide (TiO2) film, the photocatalytic degradation of endotoxin, which is a pyrogenic constituent of Escherichia coli (E. coli), as well as its bactericidal activity, was investigated. The TiO2 films were prepared from titanium isopropoxide solution, annealing at 500 °C. The bactericidal activity for E. coli cells was estimated by survival ratio calculated from the number of viable cells which form colonies on the nutrient agar plates. The endotoxin concentration was determined by the Limulus tests. When E. coli cells were killed by the TiO2 photocatalyst under UV irradiation, the endotoxin from the cells was also degraded efficiently. This result shows that the TiO2 photocatalyst has both bactericidal activity and decomposing activity for the endotoxin (i.e., detoxifying activity). The bactericidal effect of the TiO2 thin film results from both inactivating the viability of the bacteria and the destruction of the...

800 citations

Journal ArticleDOI
TL;DR: In this article, the authors reported the details of the photoconvertible surface wettability of TiO2 surfaces and showed that the formation of a microstructured composite between hydrophilic and oleophilic phases, which results from the photogenerated Ti defects at definite sites, is considered to explain the unique feature.
Abstract: The discovery of photoinduced water splitting on TiO2 electrodes has prompted extensive research on TiO2 and other semiconductor materials, which have been widely adopted as potential substances for solar energy conversion and environmental purification. Most work has focused on improving the efficiency of energy conversion or photocatalytic reactions. Little research has been reported to clarify the effect of light on the properties of TiO2 surfaces. Very recently, we found that UV illumination of TiO2 materials can generate surfaces that display 0 contact angle for both water and oily liquids. Following this finding, intensive research has been performed to explicate the mechanism of this unique amphiphilic surface character. In this communication, we report the details of the photoconvertible surface wettability. The formation of a microstructured composite between hydrophilic and oleophilic phases, which results from the photogenerated Ti defects at definite sites, is considered to account for this unique feature. The observation of the amphiphilic surfaces was initiated by the contact angle measurements of TiO2 anatase thin films. The water contact angle for a freshly prepared film averaged 15 ±1 . After the sample had been stored in the dark for 2 months, the water contact angle increased to 72 ±1 . When a water droplet touched the UV-illuminated film, it spread immediately, leaving an irregular shape on the surface with a contact angle of 0 ±1 . The contact angle of glycerol trioleate (GT), a main ingredient of edible oil, for the TiO2 surface was also measured. Prior to UV illumination, the GT contact angle averaged 10 ±1 , indicating that the surface is hydrophobic and oleophilic. Surprisingly, after UV illumination a GT droplet also spread out, resulting in a contact angle of 0 ±1 when it touched the TiO2 surface. Parallel experiments were performed using other liquid species, e.g., hexadecane, ethylene glycol, tetralin. Distinct contact angles resulted for the hydrophobic TiO2 surface. However, all of the liquids spread completely on a UV-illuminated TiO2 surface, with a contact angle of 0 ±1 . This leads to the tremendous conclusion that UV illumination has created a surface that is both highly hydrophilic and highly oleophilic. The wettability change was observed on both anatase and rutile TiO2 surfaces in the form of either polycrystals or a single crystal, independent of their photocatalytic activities. Even after the TiO2 had been stored in the dark for a few days, the high amphiphilicity of the TiO2 surface was maintained. A longer storage period induced a gradual increase in the water contact angle, revealing a surface wettability trend towards hydrophobicity. However, the high amphiphilicity was repeatedly regenerated by UV illumination. Surface wettability is generally denoted by the contact angle. According to Young's equation, the contact angle of a liquid drop on a solid surface results from the balance between the cohesive forces in the liquid and the adhesive forces between the solid and the liquid. For a certain liquid, the predominant contribution to the contact angle comes from the interfacial character of the solid material, which is related to its surface structure. Therefore, structural change of the TiO2 surface via UV illumination may play an important role in its unique wettability. Friction force microscopy (FFM) images supply information at a microscopic level to explain surface wettability. A rutile TiO2(110) single crystal was used since its wettability behavior (as induced by UV illumination) is analogous to anatase polycrystalline films. In addition, a flat surface is required for FFM measurement. Before UV illumination (Fig. 1a), no difference in contrast was observed for either the FFM image or the topographic image (not shown here), indicating microscopically homogeneous wettability on the surface. After UV illumination (Fig. 1b), however, a distribution of hydrophilic (bright) and oleophilic (dark) areas was clearly seen on the surface. Figure 1c shows a medium scale FFM image, corresponding to the framed area in Figure 1b, which illustrates hydrophilic domains with a regular rectangular shape in the range of 30±80 nm in size. A higher resolution topographic image (Fig. 1d) was also acquired, demonstrating that the hydrophilic domains are higher in position than the oleophilic areas. The image was viewed by rotating the sample stage by 45 with respect to Figure 1c, indicating that the characteristic structure is irrespective of the scanning direction. All the images show that the rectangular features align particularly along the [001] direction of the (110) single-crystal surface. As schematically illustrated in Figure 2A, oxygen bridging sites align along the same direction. It is widely accepted that the atomic coordinations at the TiO2 surface differ from those in the bulk since the atom arrangements are truncated on the surface. This gives rise to five-coordinated Ti atoms and two-coordinated O atoms, which are more energetically reactive than the six-coordinated Ti and

782 citations

Journal ArticleDOI
TL;DR: In this article, the photoinduced surface wettability conversion reactions of ZnO and TiO2 thin films were investigated by means of water contact angle measurement and X-ray photoelectron spectroscopy.
Abstract: The photoinduced surface wettability conversion reactions of ZnO and TiO2 thin films were investigated by means of water contact angle measurement and X-ray photoelectron spectroscopy. Before ultraviolet (UV) illumination, ZnO and TiO2 films exhibited water contact angles of ∼109 and ∼54°, respectively. UV illumination turned both surfaces to highly hydrophilic with water contact angles smaller than 10°. Storage in the dark reconverted the highly hydrophilic films to their original states. Reversible surface wettability conversion reactions were achieved by alternate UV illumination and storage in the dark on both the films. The similar behaviors of wettability conversion observed on ZnO and TiO2 surfaces suggest that they follow a similar conversion mechanism. Preferential adsorption of water molecules on the photogenerated surface defective sites is ascribed to the formation of highly hydrophilic ZnO and TiO2 surfaces. Achievement of highly hydrophilic ZnO and TiO2 surfaces by high-temperature annealing...

732 citations

Journal ArticleDOI
25 Jul 2000-Langmuir
TL;DR: In this paper, a transparent superhydrophobic thin film with TiO2 photocatalyst was prepared by utilizing a sublimation material and subsequent coating of a (fluoroalkyl)silane.
Abstract: Transparent superhydrophobic thin films with TiO2 photocatalyst were prepared by utilizing a sublimation material and subsequent coating of a (fluoroalkyl)silane. The transparency of the films decreased with increasing TiO2 concentration, which was attributed to the size difference of the starting materials. The film with only 2 wt % TiO2 maintained higher contact angle than the film without TiO2 after 1800-h outdoor exposure, the accumulation of stain being avoided due to TiO2 photocatalysis. The films prepared in this study are the first ones that satisfy the requirements of transparency, superhydrophobicity, and long lifetime simultaneously.

715 citations


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08 Dec 2001-BMJ
TL;DR: There is, I think, something ethereal about i —the square root of minus one, which seems an odd beast at that time—an intruder hovering on the edge of reality.
Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

33,785 citations

Journal ArticleDOI
24 Oct 1991-Nature
TL;DR: In this article, the authors describe a photovoltaic cell, created from low-to medium-purity materials through low-cost processes, which exhibits a commercially realistic energy-conversion efficiency.
Abstract: THE large-scale use of photovoltaic devices for electricity generation is prohibitively expensive at present: generation from existing commercial devices costs about ten times more than conventional methods1. Here we describe a photovoltaic cell, created from low-to medium-purity materials through low-cost processes, which exhibits a commercially realistic energy-conversion efficiency. The device is based on a 10-µm-thick, optically transparent film of titanium dioxide particles a few nanometres in size, coated with a monolayer of a charge-transfer dye to sensitize the film for light harvesting. Because of the high surface area of the semiconductor film and the ideal spectral characteristics of the dye, the device harvests a high proportion of the incident solar energy flux (46%) and shows exceptionally high efficiencies for the conversion of incident photons to electrical current (more than 80%). The overall light-to-electric energy conversion yield is 7.1-7.9% in simulated solar light and 12% in diffuse daylight. The large current densities (greater than 12 mA cm-2) and exceptional stability (sustaining at least five million turnovers without decomposition), as well as the low cost, make practical applications feasible.

26,457 citations

Journal ArticleDOI
Ryoji Asahi1, Takeshi Morikawa1, T. Ohwaki1, Koyu Aoki1, Y. Taga1 
13 Jul 2001-Science
TL;DR: Film and powders of TiO2-x Nx have revealed an improvement over titanium dioxide (TiO2) under visible light in optical absorption and photocatalytic activity such as photodegradations of methylene blue and gaseous acetaldehyde and hydrophilicity of the film surface.
Abstract: To use solar irradiation or interior lighting efficiently, we sought a photocatalyst with high reactivity under visible light. Films and powders of TiO 2- x N x have revealed an improvement over titanium dioxide (TiO 2 ) under visible light (wavelength 2 has proven to be indispensable for band-gap narrowing and photocatalytic activity, as assessed by first-principles calculations and x-ray photoemission spectroscopy.

11,402 citations